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Discussion Starter · #1 ·
Hello - I am assembling my 355 SBC with an OEM roller block. I had the block decked to zero, aftermarket Vortec heads milled, and valve job. Prior to the machine work I had this same combo running without issues using 7.187 rods and same stamped steel roller tips.

I am now trying to determine pushrod length and cannot get it right. My originals were 7.187 which puts the witness mark too far towards the exhaust. If I make it shorter using a pushrod length checker tool, the rocker nut bottoms out (runs out of thread) before I can get the pushrod short enough with the proper witness mark. Head gasket will be 0.039.

I have a feeling my rocker stud bosses need to be cut down due to the block and heads being decked, allowing me to run a shorter pushrod and ultimately proper geometry. I’ve searched all over and am ready to throw this thing in a river. Has anyone seen this?
 

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There are several things going on certainly the zero deck and the head milling moved the valve assembly on the head closer to the cam so you could see the need for a shorter push rod by that amount plus or minus and reduced or increased thickness of the head gasket compared to what you used before. The other impact is the valve job which sinks the seats and thins the valve margin which causes the valve stem to gain length when measured from the spring pad. Some shops correct this by grinding the stem tip down and shimming the spring to restore prior static pressure on the valve.

What do you mean by the head gasket will be .039, are you checking with the gasket in place? It should be.

So head gasket thickness should be there, not knowing how the valve job altered where the stem tips are in space and the milling dimensions of deck and head there is a big question as to where the valve assembly more specificall the stem tips are in dimension from the cam.

Bogie
 

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Block being decked and heads milled has the same effect as cutting the stud boss and lowering the studs, so that should have worked in your favor.

Are the heads still stock pressed in studs??
Or have they been converted to screw-in studs with a wrench hex on them? If they have a common aftermarket screw-in stud with a built in hex shoulder, then the stud bosses have to be cut down by the thickness of that wrench hex formed into the stud.
If a pushrod guideplate is used, the guideplate thickness also has to be milled off the stud boss.
 

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Discussion Starter · #4 ·
]
There are several things going on certainly the zero deck and the head milling moved the valve assembly on the head closer to the cam so you could see the need for a shorter push rod by that amount plus or minus and reduced or increased thickness of the head gasket compared to what you used before. The other impact is the valve job which sinks the seats and thins the valve margin which causes the valve stem to gain length when measured from the spring pad. Some shops correct this by grinding the stem tip down and shimming the spring to restore prior static pressure on the valve.

What do you mean by the head gasket will be .039, are you checking with the gasket in place? It should be.

So head gasket thickness should be there, not knowing how the valve job altered where the stem tips are in space and the milling dimensions of deck and head there is a big question as to where the valve assembly more specificall the stem tips are in dimension from the cam.

Bogie

The compressed thickness of the gasket is 0.039, but all checks have been without the gasket in place. The tips of the valves were also ground slightly and the shop also set spring height to the spring specs. The head gasket not in place won’t explain the drastic misalignment I’m seeing though right?

Am I on the right track with the rocker studs needing to be adjusted for all the stack up changes?
 

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Discussion Starter · #5 ·
Block being decked and heads milled has the same effect as cutting the stud boss and lowering the studs, so that should have worked in your favor.

Are the heads still stock pressed in studs??
Or have they been converted to screw-in studs with a wrench hex on them? If they have a common aftermarket screw-in stud with a built in hex shoulder, then the stud bosses have to be cut down by the thickness of that wrench hex formed into the stud.
If a pushrod guideplate is used, the guideplate thickness also has to be milled off the stud boss.
These are aftermarket summit vortecs with screw in studs, no guide plates, and the guides can accept up to 0.550 lift.
 

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Some good pictures of your set-up could be worth 1000 words here.

If you feel the heads are machined correctly, the you can use a hardened washer of the correct diameter to go between the rocker nut and the rocker ball to get you a couple of threads back if you only need a small amount.

The Summit Vortec head is cast by Dart, it is the Dart Iron Eagle Vortec without the Dart name on it....if that helps you to search out info
 

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Discussion Starter · #7 ·
This is my setup with additional spacers like you suggested. I get close to a good witness mark, but I’m nearly bottomed out on the stud.

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Looks like you are correct, the stud bosses are too tall for that style rocker stud.

Two ways to fix...
#1 - Remove head and have bosses milled down.

#2 - Switch to a straight shank screw-in stud that doesn't have a hex.

Power Products, GM Rocker Arm Studs, Chev SB 3/8", Non-Collared - Competition Products
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Mr. Gasket 1076 Mr. Gasket Screw-In Rocker Arm Studs | Summit Racing
 

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I’m assuming you’re running an OEM style roller cam?

The rockers show getting hot in the trunnion pocket, full rollers should be considered.

The rocker sure sits low on the stud, is this just a camera angle or are these really that low?

I’d put the head gasket on and recheck. Figure since zi didn’t see you milling dimensions but figure .025 gone for zero deck maybe .030 gone for head mill and .039 missing for gasket, your off almost .1 inch from where it was before these mods.

The push rod length is determined at mid lift is this how your doing it?

Bogie
 

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Discussion Starter · #10 ·
I’m assuming you’re running an OEM style roller cam?

The rockers show getting hot in the trunnion pocket, full rollers should be considered.

The rocker sure sits low on the stud, is this just a camera angle or are these really that low?

I’d put the head gasket on and recheck. Figure since zi didn’t see you milling dimensions but figure .025 gone for zero deck maybe .030 gone for head mill and .039 missing for gasket, your off almost .1 inch from where it was before these mods.

The push rod length is determined at mid lift is this how your doing it?

Bogie
Yes low lift 0.510 roller cam. Trunnions do show signs of heat. Yes length was determined at mid lift. I think I’ll give shoulderless studs a try like Eric suggested.
 

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Every Comp Cams cast steel rocker like that I've ever seen has turned blue like that, similar to how chrome moly tubing will blue with heat, or chrome headers. Still work just fine....It's just the material they are made of apparently, the alloy.

When they go black, then it'll be a problem. Did that once with solid lifter cam and 340 lb open spring pressure, those rockers were/are rated to 350 lbs max by Comp Cams....I guess i was too close.

But yeah, full rollers are a better idea.
 

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Discussion Starter · #12 ·
Every Comp Cams cast steel rocker like that I've ever seen has turned blue like that, similar to how chrome moly tubing will blue with heat, or chrome headers. Still work just fine....It's just the material they are made of apparently, the alloy.

When they go black, then it'll be a problem. Did that once with solid lifter cam and 340 lb open spring pressure, those rockers were/are rated to 350 lbs max by Comp Cams....I guess i was too close.

But yeah, full rollers are a better idea.
I’m trying to tell if the shoulder less studs will lower my whole setup as needed, or is the stud the same length as a stud with a shoulder?
 

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Are you saying that when you back the rocker adj nut off for a longer pushrod that the wheel gets farther from the center of the valve ? Did you notice how the the roller and valve stem were engaging before you tore the engine down ?
 

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Discussion Starter · #14 ·
Are you saying that when you back the rocker adj nut off for a longer pushrod that the wheel gets farther from the center of the valve ? Did you notice how the the roller and valve stem were engaging before you tore the engine down ?
Yes you are correct. Prior to tear down geometry was spot on with stock (7.187) pushrods. Now with the machined block and heads I seem to need a shorter pushrod, but my rocker studs stand too tall to allow a short pushrod. The idea is machining the stud boss to allow the stud to sit lower and run a shorter pushrod
 

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It "looks" to me like a longer pushrod "should" bring the roller closer to the center of the valve. Try loosening the nut a whole bunch and pull up on the pushrod side of the rocker. Its hard to tell for sure from your picture, but it sure looks that way to me.
 

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Discussion Starter · #16 ·
It "looks" to me like a longer pushrod "should" bring the roller closer to the center of the valve. Try loosening the nut a whole bunch and pull up on the pushrod side of the rocker. Its hard to tell for sure from your picture, but it sure looks that way to me.
It’s the opposite. This photo was taken with my checker pushrod installed, and the contact patch was still too far to the exhaust side meaning the pushrod needed to be even shorter. A longer pushrod would move the contact patch to the far edge of the valve tip.
 

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I agree with Ekinmeirbo in that looking at how I see the rocker positioned in the photos my first impression is the pushrods are too short and the whole assembly including the distance of head (and all its mounted parts) to crank centerline is/are too low. While this seems contrary to whiteness marks the amount of milling done was substantial and how much cut off the valve stems unknown. My impression in the stem height in space is too low and that lash caps and longer pushrods are needed to correct the situation. Lash caps may also require raised lip locks to move them and the spring down buying clearance for the lash caps and eliminating the need for spring shims to correct the static height.

Some other thinking than generalized whiteness mark logicons needs to be pursued.

Bogie
 

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Discussion Starter · #18 ·
I agree with Ekinmeirbo in that looking at how I see the rocker positioned in the photos my first impression is the pushrods are too short and the whole assembly including the distance of head (and all its mounted parts) to crank centerline is/are too low. While this seems contrary to whiteness marks the amount of milling done was substantial and how much cut off the valve stems unknown. My impression in the stem height in space is too low and that lash caps and longer pushrods are needed to correct the situation. Lash caps may also require raised lip locks to move them and the spring down buying clearance for the lash caps and eliminating the need for spring shims to correct the static height.

Some other thinking than generalized whiteness mark logicons needs to be pursued.

Bogie
That makes sense. Just to confirm though, I can also have the rocker stud bosses machined down too as a solution right?
 

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That makes sense. Just to confirm though, I can also have the rocker stud bosses machined down too as a solution right?
I’m not sure what you mean by machining the stud bosses down. Cutting more thread ?

Studs are made with rolled threads not cut threads as would be done by a machinist or yourself. Cut threads are not quite the same as rolled threads both in contour but in how they treat the metal. The cut thread does what it sounds, it removes metal to leave the thread pattern, rolled threads are impressed by squeezing them into the metal, no material is lost in that process, essentially they are formed by cold forging. The result is a much stronger fastener of stud in this case than results from die cutting threads. This is important when you consider how the threads and overall structure of rocker studs need to resist the loads imposed on them.

Not all studs are the same dimension as to thread length nor are they the same in overall length, I recommend you do some research on this.

In tge mean time I remain skeptical over total length of your system. The shorter push rod is going to roll the rocker such that the tip rises which will begin to move the spring retainer toward the rocker’s arm and will roll the trunnion toward the spring, Here you need to be aware of clearances which includes the stud slot on the rocker’s back side that is out of ordinary view.

In your original attached photos the contact point really isn’t all that bad, it’s tight and only slightly off center. As these things can go that really isn’t too trashy.

Bogie
 

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Discussion Starter · #20 ·
I’m not sure what you mean by machining the stud bosses down. Cutting more thread ?

Studs are made with rolled threads not cut threads as would be done by a machinist or yourself. Cut threads are not quite the same as rolled threads both in contour but in how they treat the metal. The cut thread does what it sounds, it removes metal to leave the thread pattern, rolled threads are impressed by squeezing them into the metal, no material is lost in that process, essentially they are formed by cold forging. The result is a much stronger fastener of stud in this case than results from die cutting threads. This is important when you consider how the threads and overall structure of rocker studs need to resist the loads imposed on them.

Not all studs are the same dimension as to thread length nor are they the same in overall length, I recommend you do some research on this.

In tge mean time I remain skeptical over total length of your system. The shorter push rod is going to roll the rocker such that the tip rises which will begin to move the spring retainer toward the rocker’s arm and will roll the trunnion toward the spring, Here you need to be aware of clearances which includes the stud slot on the rocker’s back side that is out of ordinary view.

In your original attached photos the contact point really isn’t all that bad, it’s tight and only slightly off center. As these things can go that really isn’t too trashy.

Bogie
I am referring to the boss in the head that the rocker stud screws into, machining that surface down so the stud sits lower in the head. In the photo you can see the rocker is basically touching the bottom of the rocker stud hex portion.
 
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